A token ring network is a system for connecting a plurality of stations in order to have each station able to communicate with all other stations. Each station has an input line and an output line. The concentrator with the media modules connect all of the lines so that signals on the output line of one station are delivered to the input line of the next downstream station. All these stations are thus connected in a line, with the output line of the last downstream station being connected to the input line of the first station. The stations are thus connected together in a ring. In order to organize the communication on the ring, a token is passed along the ring to indicate when a station can and cannot transmit onto the ring. When a station desires to transmit, it first determines if the ring is available. If the ring is available, the station transmits a frame onto the ring. The frame contains, among other things, a destination address of the station which is to receive the transmission, and a source address which is the address of the station generating the transmission. The frame then gets passed to the next downstream station. The downstream station looks at the destination address of the frame and if the frame is not destined for that station, the station then passes the frame onto the next station. When the frame reaches the destination station, the destination station reads in the data of the frame, and then continues to pass the frame along the ring. When the frame reaches the original source station, the source station removes the frame from the ring and then makes the ring available again for transmission.
One way to implement a token ring network is with a concentrator that contains one or more media modules. The media modules contain ports, and each station connects to a port in the concentrator. The media module and the concentrator connect all the ports to form the individual stations into a token ring. The concentrator provides a connection between the media modules and also performs management of the network or the several individual networks. In order to perform management, it is helpful for the concentrator to know which ports are being used and who is using them.
A concentrator also can provide a security function, in only allowing particular stations access to a particular ring network. A concentrator can also perform a statistical analysis to determine if a particular station is overloading or damaging the network. The management function of the concentrator can then identify this station in order to send a message to the station to correct a problem, or gain additional information from the station. All of these functions require knowledge of the stations connected to the ports.
The market for concentrators has been driven by the necessity to manage a large numbers of workstations in an efficient manner. One of the main functions of a networking hub is to provide network managers a map of workstations connected to each port on the concentrator. This function is commonly referred to as "Address to Port Mapping". The map created by this function associates the MAC (Media Access Control) layer address of the workstation to the physical port on the concentrator. In the production of each station, the individual station can be registered with a standards organization and a unique MAC address can be assigned to that station. That station can then use that MAC address as its own address whenever it is connected to a network and other stations can send data to the station by using its MAC address. Often the MAC layer address is then associated with physical locations and/or user names by network management tools.
The Institute of Electronic and Electrical Engineers (IEEE) has formed a well-known standard called the IEEE 802.5 communication protocol standard which is incorporated herein by reference. This IEEE 802.5 communication standard provides a general overview and background of the well-known token ring communication topology. In the IEEE 802.5 Token Ring environment, concentrators have traditionally associated MAC address with ports by monitoring Port Insertion and Neighbor Notification processes. Token Ring Stations assert or negate a DC (Phantom) current to indicate their desire to insert into or de-insert from the ring. The concentrator monitors port insertion and de-insertion to determine which ports are active.
The concentrator would typically use a centralized MAC device for each token ring, to parse the Neighbor Notification frames (Active Monitor Present and Standby Monitor Present MAC frames). The centralized MAC would filter all Neighbor Notification frames into a buffer. Software routines would then be used to match station insertions and de-insertions with newly present or newly absent participants in the Neighbor Notification process.
The centralized MAC scheme works well for rings where there is a one to one correspondence between ports and MAC stations that participate in Neighbor Notification. There are common network configurations that do not provide this one to one correspondence. One example of this is when a fanout device is in use. Fanout devices allow more than one token ring station to be inserted on a single concentrator module port. Fanout devices create a problem for centralized address to port mapping schemes because there is no longer a correspondence between station insertion/de-insertion and Phantom drive to a port. Often, centralized mapping schemes can not distinguish as to whether a station is attached to a specific port or the adjacent port on that ring.
Another situation where there is not a one to one correspondence between port insertions and a MAC address is when a "MAC-less" token ring station is inserted on a concentrator module port. Several Token Ring analysis tools fall into the category of "MAC-less" station. "MAC-less" stations monitor and repeat, but do not generate, token ring frames. As such, these devices do not participate in the Neighbor Notification process, and cannot provide the information required to assemble an address to port map. Thus, centralized mapping schemes can not distinguish the attachment of adjacent stations in the presence of MAC-less stations.
U.S. Pat. No. 5,319,644 describes a method and apparatus for identifying port/station relationships in a network. In this reference, three lists are formed. A sequential list of all the active ports is formed, a sequential list of all the active stations is formed, and then a sequential list of all the end stations in a port are formed. Using these three lists, it can be determined which stations are connected to a particular port. This method requires a centralized entity to form all of the lists. Having a single centralized entity perform all of the work required to associate an address with a port, requires that the centralized entity be made capable of handling the maximum number of modules and ports connectable to a concentrator. Concentrators are very adaptable with regard to the number of ports which they can support, and therefore a centralized entity may have to be made very capable. Much capacity would be wasted if the concentrator was only partially used. Also, if a large number of active ports are being supported by the concentrator, the centralized entity must perform much work, which could possibly detract from other management functions that the concentrator performs. However, U.S. Pat. No. 5,319,644 is very informative with regard to the state of the art and is incorporated by reference.
U.S. Pat. No. 5,361,250 is also very informative with regard to the state of the art and is incorporated by reference.